Method for processing discharge lamps



Se t. 27, 1966 w. v. CUSHING 3,275,397

METHOD FOR PROCESSING DISCHARGE LAMPS Filed Aug. 22, 1963 5 f I if? 515 r A I WITNESSES INVENTOR mm W Walter v Cushing ATTORNEY United States Patent 3,275,397 METHOD FOR PROCESSING DISCHARGE LAMPS Walter V. Cushing, Verona, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 22, 1963, Ser. No. 303,771 5 Claims. (Cl. 316-25) The present invention relates to electric lamps of the high pressure mercury vapor type wherein light is pro duced by a discharge between electrodes and has particular reference to the method of processing such devices to prevent the voltage required to initiate a discharge in the lamp from becoming excessive.

In high pressure mercury vapor lamps, particularly in those types in which metallic composition additives are employed to increase the lumen output of the emitted radiations, it frequently happens that initially these lamp types are exceptionally difficult to start even after thorough seasoning during fabrication of the lamp. This accordingly requires a much higher starting voltage than desirable until the lamps have been in actual use for an appreciable time, after which the starting voltage falls to that desired. This tendency toward too high starting voltage can be materially reduced by extended seasoning of the lamp, which is meant that it is operated immediately following its fabrication for a substantial period of time. Such extended seasoning, however, adds greatly to the manufacturing costs of such a lamp because of the increased time and expense involved.

It is accordingly the primary object of the present invention to provide a method for initially reducing the starting voltage for high pressure mercury vapor lamps pfiwided with metallic composition additives, to a desired v ue.

Another object of the present invention is the provision of an accelerated seasoning method which initially reduces the starting voltage for a high pressure mercury vapor lamp having metallic composition additives, to a desired value during actual fabrication of the lamp.

The foregoing objects of the present invention, together with other objects which will become apparent from the following description, are achieved by first seasoning the lamp in the usual manner and thereafter applying a voltage between the starting electrodes to initiate and sustain a discharge therebetween, with current flow being limited to a value sufficient to heat such starting electrodes to a high temperature below their melting point for an adequate time period to cause impurity gettering of the completed lamp.

The present invention can be readily understood by those skilled in the art by reference to the accompanying drawing wherein the single figure is a schematic illustration of a high pressure mercury vapor lamp employing metallic composition additives as part of the discharge supporting medium and showing the electric circuitry employed during initial fabrication of the lamp to reduce the starting voltage otherwise required to initiate a discharge between the operating electrodes thereof.

Referring now to the drawing, a high pressure mercury vapor lamp 5 is therein shown which is provided with the customary pressed seals at each end. A pair of main discharge supporting electrodes 6 and 7 are provided at each end of the lamp which may be formed of coiled tungsten wire surrounding an electron emissive material, as is well known in the art. Also disposed at each end of the lamp 5 adjacent the main discharge supporting electrodes 6 and 7 are starting electrodes 8 and 9 which comprise a metallic rod of a refractory metal which will getter gaseous impurities when heated to high temperatures, such as tungsten, tantalum, or the like. Lead-in conductors extend from each of the main and starting elec- 3,275,397 Patented Sept. 27, 1966 "ice trodes outwardly through the ends of the lamp envelope being sealed by molybdenum ribbon or the like 10 to the respective pressed seal ends of the lamp 5. The lamp 5 is provided with an inert ionizable medium, such as argon, neon, or the like, to facilitates the starting of a discharge and the interior of the envelope is also provided with a small quantity of a vaporiza-ble material such as mercury, together with a metallic composition additive as sodium-iodine, thallium-iodine, or the like, to increase the luminous output of the discharge. Such so-called additive lamps are disclosed in copending application, Serial No. 188,368, filed April 18, 1962, and owned by the present assignee.

During fabrication of the lamp and following its complete assembly it is subjected to the customary seasoning cycle by the initiation of a discharge between the main electrodes thereofto thus heat the latter and drive off occluded gases therefrom. However, it has been found that with these metal vapor lamps employing metallic additives, such as previously mentioned, and despite proper seasoning thereof to establish a desired starting voltage, that after an exceedingly short period of usage the starting voltage has heretofore increased to an unstaisfactory magnitude. To obviate this undesired tendency toward increased starting voltage, in accordance with the present invention these additive metal vapor lamps are seasoned in the usual manner by establishing and maintaining an arc discharge between the main electrodes 6 and 7 for a predetermined period of time, such as from fifteen to thirty minutes, after which the are preferably is extinguished and the lamp preferably allowed to cool.

Thereafter the starting electrodes 8 and 9 are then connected to a supply source Ll-L2 and an arc discharge is initiated therebetween by increasing the voltage of the source L1-L2 and utilizing a high frequency induction coil to cause ionization of the gaseous medium within the lamp 5. Current flow through the lamp is limited by a series connected resistor 12 which holds the current to a value such as to heat these starting electrodes to a high temperature below their melting point and the discharge is maintained for a predetermined short period of time such as ranging from a few seconds to a minute or two suflicient to completely getter the finished lamp. Accordingly, these high temperature metallic starting electrodes act as getters which absorb the gaseous impurities liberated by the main electrodes and other portions of the arc tube during the customary seasoning as previously mentioned. The voltage required to start an arc discharge within the lamp is thus initially established at a sufficiently low and substantially constant value that no difficulty of increase in starting voltage is thereafter experienced during lamp life.

It should thus become obvious to those skilled in the art that a method has become herein provided for initially establishing a sufficiently low and substantially constant starting voltage for a high pressure mercury vapor lamp employing metallic additives as a vaporizable material that no difficulties of increase in starting voltage are thereafter encountered. Moveover, such initial establishment of a desired low starting voltage is achieved without the neces-. sity of extended and costly seasoning.

As a possible alternative embodiment for practicing the present invention, the arc as initially established and maintained between the main operating electrodes could be switched directly to the starting electrodes to getter the gaseous impurities, without first allowing the lamp to cool.

Although one specific embodiment of the present invention has been herein shown and described, it is to be understood that still further modifications thereof may be made without departing from spirit and scope of the invention.

sired substantially constant value, which lamp has a radia tion transmitting envelope and main operating electrodes and starting electrodes disposed within and proximate to each end of the envelope, which method comprises,

(a) initially seasoning said lamp by establishing an arc discharge between the main are supporting electrodes of said lamp and maintaining the established disohargefor a predetermined period of time,

(b) and thereafter discontinuing the discharge between the main electrodes and maintaining a discharge for a predetermined short period of time between the starting electrodes disposed at each end of said lamp to cause the starting electrodes to, getter gaseous impurities within the lamp.

2. The method of initially reducing the starting voltage of a high pressure mercury vapor additive lamp to a desired substantially constant value, which lamp has a lighttransmitting envelope and main operating electrodes and starting electrodes which will getter gaseous impurities when heated to high temperatures disposed within and proximate to each end of the envelopes, which method comprises,

(a) initially seasoning said lamp by establishing and maintaining an arc discharge between the main arc supporting electrodes of said lamp for a period of from fifteen to thirty minutes,

(b) discontinuing said discharge and allowing the lamp to cool,

(e) and thereafter establishing a discharge for a short period of time ranging from a few seconds to two minutes between the starting electrodes disposed at each end of said lamp to cause the starting electrodes to getter gaseous impuritieswithin the lamp.

3. The method of initially reducing the starting voltage of a high pressure mercury vapor additive lamp to a desired substantially constant value, which lamp has, an elongated light-transmitting envelope, and main arc-supporting electrodes and starting electrodes which will getter gaseous impurities when heated to high temperatures positioned within and proximate to each end of the envelope,

which method comprises,

(a) initially seasoning said lamp by establishing and.

(b) discontinuing said discharge and allowing the lamp to cool,

(0) connecting the starting electrodes at each end of said lamp to a source of supply,

(d) and raising the voltage of such supply source to a value sufiicient to initiate a discharge for a predetermined short period of time between the starting electrodesto heat them to a high temperature below their melting point to cause the starting electrodes to getter gaseous impurities within the lamp. r

4. The method of initially reducing the starting voltageof a high pressure mercury vapor additive lamp to a de-, sired substantially constant value, which lamp has "an elon- :v gated light-transmitting envelope and main arc-supporting electrodes and starting electrodes which will getter gaseous impurities when heated to high. temperatures positioned within and proximate to each end of the envelope, whichf method comprises,

(a) initially seasoning said lamp by establishing an arc discharge between the main are supporting electrodes of said lamp and maintaining the established dis: charge for a predetermined period of time,

(b) discontinuing said discharge and allowing the lamp to cool,

(c) connecting the starting electrodes at eachend of said lamp to a source of supply,

(d) and raising the voltage, of such supply source to initiate a discharge for a predetermined short period of time between the starting electrodeswhile limiting the discharge current to a value sufiicient to heat said starting electrodes to a high temperature just below their melting point to cause the starting electrodes to getter gaseous impurities within the lamp.

5. The method of initially reducing the starting voltage of a high pressure mercury vapor additive lamp to a desired substantially constant value, which lamphas an 1 elongated light-transmitting envelope and main arc-supporting electrodes and starting electrodes which will get r ter gaseous impurities when heated to high temperatures positioned within and proximatewto each end of theten- I velope, which method comprises,

(a) initially seasoning said lamp by establishing an arc discharge between the main arc-supporting electrodes of said lamp and maintaining the are for a period of ranging from a few seconds to two minutes between .the starting electrodes While limiting the discharge current to a value sufiicient to heat said starting electrodes to a high temperature just below their melting point to cause the. starting electrodes to getter oc cluded gases within the lamp.

No references cited.

FRANK E. BAILEY, Primary Examiner. 

1. THE METHOD OF INITIALLY REDUCING THE STARTING VOLTAGE OF A HIGH PRESSURE MERCURY VAPOR ADDITIVE LAMP TO A DESIRED SUBSTANTIALLY CONSTANT VALUE, WHICH LAMP HAS A RADIATION TRANSMITTING ENVELOPE AND MAIN OPERATING ELECTRODES AND STARTING ELECTRODES DISPOSED WITHIN AND PROXIMATE TO EACH END OF THE ENVELOPE, WHICH METHOD COMPRISES, (A) INITIALLY SEASONING SAID LAMP BY ESTABLISHING AN ARC DISCHARGE BETWEEN THE MAIN ARC SUPPORTING ELECTRODES OF THE SAID LAMP AND MAINTAINING THE ESTABLISHED DISCHARGE FOR A PREDETERMINED PERIOD OF TIME, 